407 
“ It is a common notion, and one popularly believed to be unanswerable, 
that the calculations of the positions of the planets, the periods of the comets, 
the times of eclipses, and other astronomical problems solved by the applica- 
tion of Newton’s beautiful theory of gravitation to orbital motion, and so 
marvellously confirmed by the actual observation of the phenomena in the 
heavens themselves, essentially require, as their starting-point, the supposi- 
tion of the earth’s absolute motion round the sun. 
“ That this is not a true notion will appear evident, simply from this, that 
astronomers actually make some of these calculations on other hypotheses. 
“ The mathematician, before commencing his calculation of the motion of 
a heavenly body, is obliged to seek for some point either really fixed in space, 
or, if that be impossible, to suppose some point to be fixed : such a point is 
commonly called the origin of co-ordinates 
“Practically, indeed, the astronomer chooses the origin of co-ordinates 
quite arbitrarily, placing it where he will be able most easily to simplify the 
analytical process which any particular investigation requires. 
“ Thus, for example, in the planetary theory . . . the centre of the sun is 
taken as the fixed point, and the earth, together with all the other planets, 
are supposed to revolve round it. 
“ On the contrary, in the lunar theory the centre of the earth is chosen as 
the fixed point, &c 
“ Again, in Goodwin’s 1 Mathematical Course,’ art. 12 of the section on 
astronomy [this passage occurs] : ‘ According to observation, the sun appears 
to move round the earth ; but the phenomena will be exactly the same 
whether the earth moves round the sun, or the sun round the earth.’ .... 
“ The practice, then, of astronomers favours neither theory, and ignores the 
question of absolute motion altogether, recognizing merely that which is 
relative .” (Pp. 3—6.) 
40. Afterwards, the “ Wrangler 39 goes on to ask and to 
answer a question, which will probably astonish all who hear 
or read this paper much more than anything I have yet said. 
He asks : — 
“ Has it ever been demonstrated that the earth revolves round its own 
axis ? ” [And his answer is] “ I must reply in the negative, and assert, more- 
over, that we shall not find that its demonstration is claimed in any truly 
scientific treatise, although by every one its revolution [he meSns rotation] 
is assumed to be a most probable truth.” (P. 26.) 
Again, he goes on : — 
“ Should, then, the earth be at rest on its own axis, the only alternative 
we have is to suppose a revolution of the whole heavens in the short space of 
twenty-four hours. 
“ Startling as this is, we have seen that it has not been demonstrated to be 
mechanically impossible, as far as the terrestrial phenomena are concerned ; 
